The Charity Commission has confirmed it will be speaking to the NBH after receiving "a dozen-or-so complaints". The charity's latest accounts were nearly seven months late, it said. One of the charity's patrons has also resigned.

Christine Pratt, founder of the helpline, contacted the BBC at the weekend to say that several No 10 staff had been in touch. She said she went public because she was angered when ministers denied claims of bullying made in a new book by Observer journalist Andrew Rawnsley.

Rekha Wadhwani, chief executive of The Helplines Association, said the NBH was not an association member and she was very disappointed by the breach of confidentiality.

"We are all about giving trust to callers," she said. "It takes a lot of effort to pick up the phone, and you can only do it if you are sure it won't be all over the TV and radio.

"This is a breach of confidence on a big scale. Within the organisation people will be going round thinking, was it you, or you or you?"

Wadhwani said the episode might damage the work of helplines in the short term, but hoped it would mean the public would make sure services they used were properly accredited.

She would approach the National Bullying Helpline to offer help with its policies and procedures.

It said: "We're disgusted and upset and we're writing to the Charity Commission today to complain about the National Bullying Helpline.

"In the meantime, we suggest Mrs Pratt considers her position, given the damage she has caused to the anti-bullying sector where confidentiality is paramount."

Emma-Jane Cross, chief executive of the charity Beatbullying, declined to comment. "We're absolutely not getting involved in this," she said.

A spokeswoman for the Charity Commission said it was considering whether it had any role in the row.

"A number of issues have been raised over the weekend concerning the charity National Bullying Helpline and we have received a number of complaints," she said. "We will be contacting the charity for further information."

A spokeswoman for Cooper said it was because he felt it was unacceptable for Pratt to disclose details of the organisations whose staff had called the helpline.

The National Bullying Helpline's website says it has a "clear privacy policy". It says: "We do not share your details with anyone".

The helpline was started in 2002 and was registered as a charity in 2007. The only accounts it has filed with the Charity Commission show income of £1,818 and expenditure of £852 for the year to September 2007.